This invention relates generally to photocopiers and in particular to an apparatus and method for correcting a paper misfeed in such copiers.
One of the mechanical problem areas of major concern to the copier industry is the misfeeding or jamming of copy sheet material. In normal operation, a sheet of copy material is applied against the photosensitive surface, most often the outer perihery of a drum-shaped member, and the image is transferred to the sheet. The sheet thereafter is removed from the drum and either dried or fused, depending upon the particular development process which is used. A jam condition can, for example, occur just after the step of the copying process when a developed image on the moving photosensitive surface is transferred to a sheet of copy material. In the jam or misfeed condition, a "pick-off" of the sheet material is missed and the copy sheet improperly remains on the photosensitive surface.
Such a condition must be detected and corrected so that the photosensitive surface and the operating stations adjacent the photosensitive surface, are neither damaged nor rendered inoperable due, for example, to toner contamination. To this end, there may exist many techniques for detecting the undesired presence of sheet material, or its absence, at one or more processing stations in the copier.
In most typical situations when the copier control circuitry is "informed" that a misfed sheet has occurred, the photosensitive surface immediately is rendered inoperative by a braking procedure, the copier is shut down, and either the operator or a service man must correct the jam condition by removing sheet from the copier. When the jam involves paper adhering to the drum member, that is a failure in the "pick-off" mechanism, it may be necessary to remove the drum from its mount, a procedure best performed by trained technicians. The down-time of the copier and the service call are expensive to the user.
In an attempt to avoid this expense of both time and money, several techniques have been developed to avoid the need for a service call. Thus, for example, the detection of the misfeed may operate to enable a back-up sheet removal system to strip the sheet from the photosensitive surface. In these systems, however, although the paper is removed from the drum, the equipment is complex, sensitive to dimensional variations, and increases the physical size of the copier system.
In the 1970's, liquid transfer development systems were first introduced commercially. These systems employ a developer consisting of a clear liquid containing finely divided toner particles. This development system differs significantly from earlier commercial systems wherein the toner was a dry mixture of carrier particles and a toner material. The liquid developer system concept has most often been applied to small, relatively low-cost machines, and hence, it is not economically feasible to provide a back-up sheet removal system due to the dual requirements of added physical space and additional expense. Thus, machines employing a liquid developer, wherein the copy sheet tenaciously adheres to the wet photosensitive surface, provide added incentives to improve the jam detection and paper removal techniques.
It is, therefore, a principal object of this invention to provide a sheet detection and clearance apparatus and method for a photocopier wherein paper improperly adhering to a photosensitive surface after "pick-off" failure can be quickly and easily cleared. A further object of the invention is to provide a paper jam detection and clearance apparatus and method which are reliable, simple to operate and use, low in cost, which do not require complex apparatus, and can make use of existing apparatus on the copier. A still further object of the invention is to provide such an apparatus and method which are particularly useful in liquid toner transfer systems, and which provide an operator with easy access to the sheet material to be removed when a jam condition occurs.